"Overlappingly overstrikeable ribbons", which are particularly intended for type wheel printers are known. The term "overlappingly overstrikeable" means that the ribbon transfer per strike which is normally somewhat more than one character width is reduced to a fraction of the character width, e.g. to 1/3 or 1/5, so that each strike only impinges on a fresh area of the ribbon with a small surface proportion, whereas the larger surface proportion of the character strike is on a ribbon area which was struck once or several times before. Such typewriter ribbons are also called "overstrike" ribbons. Such a ribbon, like a single-pass ribbon, only is moved in one direction, but is still utilized several times. Compared with repeatedly overstrikeable ribbons which have to be correspondingly moved forwards and backwards (with a full displacement of approximately one character width per strike), this procedure obviates the complicated and troublesome reversing mechanism required for changing the ribbon running direction.
In order to obtain high overstrike figures, it has hitherto been considered necessary to incorporate into the ink-releasing coating of an overlappingly overstrikeable ribbon fillers, particularly with large inner surface and a small particle size distribution of e.g. 0.2 to 20 micrometers. The fillers fulfill a number of functions and in particular serve to increase to productivity of the ribbon. It was also hitherto considered necessary to integrate the oil-based ink paste into a plastic matrix.
These requirements applied regardless of whether the particular overlappingly overstrikeable ribbon for the printing process was used with a type wheel printer, as a winding spool or as a continuously full cassette. Only as a result of this special construction, i.e. plastic matrix with filler, together with the coloring constituents and the oil, was it considered possible to permanently increase the ink supply for the printing process and thereby obtain the desired overstrike values. Reference is made to German Pat. Nos. 32 14 305 and 33 07 432 relative to the above prior art.
It could be asumed that excessively thick ink coatings would not be able to ensure a constant ink supply. Since a ribbon of this type wound up into a reel would be expected to have an "oiling out" tendency, i.e. there would be wetting of the engaging back of the winding. This wetting could lead to a sticking of the winding spool and to transfer problems in the cassette. This sticking could also occur if the ambient temperature rose greatly e.g. in excessively heated rooms.